The present invention relates to microwave powered lamps having improved cooling of magnetrons therein.
FIG. 1 illustrates a prior art microwave powered lamp 10 of the type sold by the Assignee of the present invention, The microwave powered lamp may be used to produce ultraviolet (UV) or visible light depending on the application such as, but not limited to, curing surface coatings. A magnetron 12 provides microwaves transmitted through a microwave cavity 14 to a microwave powered bulb 16 which outputs light as stated above in either the UV or visible spectrum depending upon the application. An air source 18 blows air 20 through a housing 22 which contains the magnetron 12, microwave cavity 14. and microwave excited bulb 16. As indicated, air 20 flows through the housing around the magnetron 12 to provide cooling thereof and into the microwave cavity 14 and to and around the bulb 16 to provide cooling of the bulb. The lamp housing 22 is designed to channel air 20 in contact with cooling fins (not illustrated) of the magnetron 12, through openings 24 and then through openings (not illustrated) of reflector 26 past the bulb 16 as described above and out of the housing 22. The air 20, which is heated by the magnetron 12 and the bulb 16, exits through the opening 29 through which the light is also outputted after being reflected by reflector 28.
The power of the light output produced by the bulb 18 is limited by the cooling of the magnetron 12. The anode (not illustrated) of the magnetron 12 is maintained during operation at a temperature of around 180 EC by the air 20 which is blown past the cooling fins. A three kilowatt magnetron is currently the maximum power commercially available magnetron which may be air cooled.
Water cooled magnetrons have been developed which have a water channel mounted in thermal contact with the outside of the anode instead of the aforementioned cooling fins utilized with the air cooled magnetron 10 of FIG. 1. Water is pumped through the water channel to cool the magnetron. The use of water to cool the magnetron is a much more effective cooling mechanism than air cooling and permits the anode temperature to be maintained at the much lower operating temperature of about 90 EC. A lower operating temperature increases the magnetron life which signiflcantly reduces the customer""s cost of ownership for the microwave powered lamp. Furthermore, water cooled magnetrons permit the use of higher input microwave power to the bulb which provides a higher power light output per linear inch of the microwave excited lamp.
Historically, water cooled magnetrons used in microwave excited lamps require an operator provided external source of cooling water for each microwave lamp, such as from an external water circulating system, fabricated to the site requirements of the microwave excited lamps. The required plumbing to add the external water circulating system substantially increases the cost to the operator to have a water cooled microwave excited lamp.
The present invention is an improved microwave powered lamp which utilizes a water cooled magnetron having a water supply circuit integrated into the microwave powered lamps. The integration of the water supply circuit into the microwave powered lamp eliminates the problem of the prior art which required an external water circulation circuit. The present invention uses a single forced air source to cool the heated water produced from cooling the magnetron and the microwave excited bulb. As a result, the entire assembly of a microwave powered lamp, including a water cooled, magnetron in accordance with the invention, is totally integrated with the microwave lamp which permits low cost installation including a group of water cooled microwave excited lamps ganged together. One or more water-cooled microwave excited lamps may be installed for curing applications to provide higher power light output, when compared to air cooled microwave excited lamps, without any consideration being given to providing an external water supply and/or cooling thereof.
The microwave powered lamp of the invention includes a housing containing a water cooled magnetron; an air source which blows air to the magnetron and the microwave excited bulb with the air providing cooling to the bulb to control the operational temperature thereof; and a heat exchanger disposed in the housing, with air blown from the air source contacting the heat exchanger. A portion of the heat exchanger is contacted by water heated by operation of the magnetron with air blown from the air source cooling the heated water. A water circulation circuit circulates heated water from the water cooled magnetron to the portion of the heat exchanger and cooled water from the portion of the heat exchanger back to the magnetron. The aforementioned water cooled microwave excited lamp may be ganged into an assembly containing multiple water cooled microwave excited lamps which each are self-contained which permits an in-line assembly of multiple microwave powered lamps all having integrated water cooling for curling an in-line target
The heat exchanger may be a radiator similar to that found in an automobile heater core with the cooling air being blown through the heater core to cool the water and then blown into the microwave cavity and through the reflector to cool the microwave excited bulb. Water flow is maintained continuously through the magnetron and the heater core using a water pump and overflow holding tank which are sized for the cooling requirements of the magnetron and may be In typical applications small and integrally mounted to the exterior of the housing of the microwave excited lamp permitting the entire assembly to be deployed without any external water connections as a single unit or a ganged assembly.
The invention provides a substantial reduction in anode temperature of the magnetrons, such as approximately 50% in a typical UV curing application, with no increase in forced cooling air requirements to provide the increased cooling of the magnetron beyond the cooling air requirement utilized for an air cooled magnetron having a substantially lower power light output. Furthermore. the life of the magnetrons is substantially increased. The extension in operating life is in general proportional to the reduction in the operating temperature, e.g. from the normal 180 EC of an air cooled magnetron, to approximately 90 EC for a water cooled magnetron, may result in doubling the life of the magnetron. Furthermore, in a preferred commercial application, a five to six kW commercially available water cooled magnetron may be utilized to excite a bulb producing a substantially higher light output.
The invention is a microwave powered lamp including a housing containing a water cooled magnetron, the water cooled magnetron providing microwaves to a microwave excited bulb, the microwave excited bulb providing light from the housing; an air source, coupled to the housing, which blows air to the water cooled magnetron and the bulb with the air providing cooling to the bulb to control operational temperature thereof; a heat exchanger, disposed in the housing, with the air blown from the air source contacting the heat exchanger, the heat exchanger having a portion contacted by water heated by operation of the magnetron with the air blown from the air source cooling the heated water; and a water circulation circuit, coupled to the water cooled magnetron and the portion of the heat exchanger, which circulates heated water from the water cooled magnetron to the portion of the heat exchanger and cooled water from the portion of the heat exchanger back to the magnetron. The portion of the heat exchanger may be a core through which water flows and the heat exchanger may be a radiator having openings through which the air flows within the housing. A water pump may be coupled to a water tank with the heated water being pumped from the water cooled magnetron through a conduit of the water circulation circuit to the portion of the heat exchanger and the cooled water being pumped from the portion of the heat exchanger through a conduit of the water circulation to one of the water tank and the water pump and the cooled water may be pumped by the pump through a conduit of the water circulation to the water cooled magnetron circuit. The water pump and water tank may be located outside the housing, The air source may be a single air blower which provides all air blown in the housing to the water cooled magnetron and to the bulb. The rate of blowing air through the housing may be chosen to maintain operation of the bulb within a temperature range within which the bulb of the lamp is designed to operate and a rate of water flow through the water circulation circuit may be chosen to maintain operation of the water cooled magnetron within a temperature range within which the water cooled magnetron is designed to operate. The bulb may be a UV bulb.
The invention is also an assembly of microwave powered lamps having the lamps therein in line. Each of the microwave powered lamps includes a housing containing a water cooled magnetron, the water cooled magnetron providing microwaves to a microwave excited bulb, the microwave excited bulb providing light from the housing; an air source, coupled to the housing, which blows air to the water cooled magnetron and the bulb with the air providing cooling to the bulb to control operational temperature thereof, a heat exchanger, disposed in the housing, with the air blown from the air source contacting the heat exchanger, the heat exchanger having a portion contacted by water heated by operation of the water cooled magnetron with the air blown from the air source cooling the heated water; and a water circulation circuit, coupled to the water cooled magnetron and the portion of the heat exchanger, which circulates headed water from the water cooled magnetron to the portion of the heat exchanger and cooled water from the portion of the heat exchanger back to the magnetron. In each microwave powered lamp, the portion of the heat exchanger maybe a core through which water flows and the heat exchanger may be a radiator having openings through which the blown air flows within the housing. In each microwave powered lamp the water circulation circuit may comprise a water pump coupled to a water tank with the heated water being pumped from the water cooled magnetron through a conduit of the water circulation circuit to the portion of the heat exchanger and the cooled water may be pumped from the portion of the heat exchanger through a conduit of the water circulation circuit to one of the water tank and the water In the tank and the cooled water may be pumped by the pump from the water tank through a conduit of the water circulation circuit to the water cooled magnetron. In each microwave powered lamp, the water pump and water tank may be outside the housing, In each microwave powered lamp, the air source may be a single air blower which provides all air blown in the housing to the water cooled magnetron and to the bulb. In each microwave powered lamp, the rate of blowing air through the housing may be chosen to maintain operation of the bulb within a temperature range within which the bulb is designed to operate and a rate of water flow through the water circulation circuit may be chosen to maintain operation of the water cooled magnetron within a temperature range within which the water cooled magnetron is designed to operate. In each microwave powered lamp the bulb may be a UV bulb.